aerobat77, Re “… what am I missing.” It’s more general than that, like what we – many pilots in the industry are missing.
Wind speed is a significant factor in landing distance because the effect of wind may not be a 1:1 relationship with distance (GS) as you imply. Thus, one of the reasons that only 50% of the headwind can be claimed as benefit, but 150% of tailwind has to be accounted for as a hazard.
An example of some of the aspects see -
AC 91-71 Runway Overrun Prevention. Considering the effect of high airspeed on distance (table 2), the addition is 30 ft/kt; however the effect of high airspeed on the tendency to float is 250ft/kt. Furthermore, these distances might be additive. Thus it is important to consider the landing distance increase when making approach/threshold speed additives.
There are similar considerations for tailwinds except the effect is much more – hence 150%. Note the significant number of overrun accidents that have involved a tailwind.
The point about commercial operations is interesting. Many pilots use the dispatch planning data for arrival data – weight, etc; - all in limits – a standard operation.
However, if this mindset is carried over to tailwind operations without checking the distance required, then a rapidly decreasing safety margin can be missed. Landing distance should always be checked (not just weight); this also provides a guide of how hard you need to brake as well as the accuracy required in the landing speed and position.
Note that EASA has identified the ‘failure to calculate landing performance’ as a safety factor in their recent analysis, also see –
Lessons from Landing Excursions.
P.S. you mentioned the BAe146 (#12) - IIRC the manufacturer’s landing tests were based on a 5 deg approach with a target touchdown rate of 6 ft/sec to determine the airborne portion of landing distance. At least five pilots had to provide data to enable a suitable average; in addition a UK CAA pilot flew some check landings, and many more landings were observed by CAA flight test engineers. Some ground roll / braking distance measurements were included in these tests, but additional data was gained from full braked landings on different runway surfaces in conjunction the anti-skid tests which also included checks in damp / wet conditions.